Dewaxing system



R. N. GILES DEWAXING SYSTEM Oct. 16, 1934.

Filed Dec. 27, 1952 ATTORNEY N-Gz'les S Q B EE N \mbubonuww INVENTOR SNB B090 mm as 3 L S QQ Q L E QN kw Patented Oct. 16,1934 I 1 UNITEDSTATES DEWAXING SYSTEM Roy N. Giles, Casper, Wyo., assignor to StandardOil Company, Chicago, Ill., a corporation of Indiana ApplicationDecember 27, 1932, Serial No. 648,846

3 Claims.

This invention relates to a dewaxing system and it pertains moreparticularly to a system for the separation of wax from petroleumlubricating oilsby means of liquefied normally gase- 5 onediluent-refrigerants such as propane.

The latest improved method of separating wax from petroleum lubricatingoils, particularly from heavy distillate stocks, is the. so-calledprocess of propane dewaxing. The waxy oil is completely dissolved in alarge excess of propane so that both oil and wax are in solution; thesolution is then cooled by the vaporization of. a part of the diluent,thereby causing the wax to solidify or crystallize in readily separableform, the solidified wax is mechanically separated from the diluted oilby means of filtration, settling, etc., and finally, the propane isrecovered from both the wax and the wax-free oil, condensed, andreturned to storage tanks for reuse.

The object of my invention is to provide a method and means of coolingthe diluted lubricating stock so that the wax will crystallize out inreadily filterable or separable form and to thereby increase the yieldof finished oil, provide a finished oil of low pour point, and expeditethe mechanical separatiorf of wax from the diluted oil. A'further objectis to minimize compressor costs and toutilize more effectively therefrigeration which is available in the system. In other words, theobject isto effect a saving of steam, a saving of condenser water, asaving of compressor costs, etc., and at the same time to effect thecrystallization of wax in readily separable form (avoiding shockchilling).

, I have discovered that .if a solution of oil and wax in propane comesin contact with a metal surface or a body of liquid which is at aconsiderably lower temperature, the wax will solidify 40, ahnostinstantaneously in the form of almost imperceptible fine crystals. Ihavefound that the formation of such crystals is veryundesirable-particularly where the separation of wax from diluted oil iseffected by filtration, and I have found that once these undesirablesmall crystals are formed it is practically impossible to remedy thesituation. It might be supposed that these crystals would subsequentlydissolve, or act as nuclei for the formation of larger crystals, orcoalesce, or in some other way .be transformed into a more desirablestructure.

-Experience has shown, however, that such a reformation of crystalstructure is ractically impossible andthat from a commercial standpointit is necessary to avoid what may be called shock chilling".

When oil is diluted with naphtha or other liquid solvents and chilled bymeans of the brine coils of an ammonia refrigeration plant, 0 thetemperature must be lowered very slowly, only a few degrees an hour;otherwise the temperature differential between the diluted oil and thebrine coil will be too great and there will be shock chilling at thesurface of the brine coil. 5 When propane is used as a refrigerant andis evaporated directly from the diluted oil, the cooling may be aboutfifty or sixty times as fast aswas possible with brine coolers-it may befrom about one-half to eight degrees per minute, preferably about threedegrees per minute. However, when a solution of waxy oil in propane hitsa cold metal surface or any cold body, there is an instantaneous coolingof the mixture at a theoretically infinite rate or, in other words, foran extremely small fraction of a second the cooling rate may be severalhundred degrees per minute. This results in shock chilling and it causesthe formation of wax crystals which are so fine that they can- 30 not bereadily removed from diluted oil by filtration and/or other mechanicalmeans. The object of my invention is to prevent this shock chilling in apropane dewaxing system.

In practicing my "inventionl prefer to obtain complete solution of bothoil and wax in propane before I: begin the chilling step. Thereafter Iam careful in transferring the diluted oil-wax mixture to see that itdoes not come in contact with any metal surface or any body of liquidwhich is at an appreciably lower temperature and which would thereforecause shock chilling.

In a preferred embodiment of my invention I heat chill chambers andconduits by condensation of propane therein between the cooling ofsuccessive batches. When a cold wax slurry has been withdrawn from achill chamber, that chamber is necessarily cold,I warm it up prior tothe introduction of a fresh charge by merely allowing Warm propanevapors to condense 1 therein, the condensed propane remaining to serveas additional diluent and refrigerant for the next batch to be cooled.

I may, in fact, employ a plurality of chill chambers arranged so thatthe first may be dis- 1 5 charged by gravity into the second, etc. Whenthe second chiller has been cooled by evaporative refrigeration and thecharge has been removed to the third chiller, the top ofthe secondchiller is connected to the vapor space of the first chiller so that thevapors leaving the first chiller to effect the cooling thereof arecondensed in the second chiller and thereby heated to the sametemperature as that to which the first chiller is cooled. Whenequilibrium is reached the slurry is passed from the first chiller intothe second chiller, and the next step of cooling is effected byvaporizing propane from thesecond chiller and condensing it in the thirdchiller which is quite cold due to the previous charge which was justremoved therefrom. By operating in this manner shock chilling isavoided, compressor costs are reduced to a minimum, and a marked savingin steam and condenser water is effected. Furthermore, this type ofcooling obviates the necessity of using an expensive variable compressorwhich has heretofore been required to reduce the pressure in a chillchamber from about 170 pounds/square inch to 0 pounds gauge.

The invention will be more fully understood from the following detaileddescription and from the accompanying drawing which forms a part of thisspecification and which diagrammatically represents my improved system.

In describing myinvention I will refer to the separation of wax from'aheavy lubricating distillate from Mid-Continent crude, the distillatehaving been acid treated and neutralized but not clayed, and having aviscosity of about seconds Sa'ybolt at 210 F. It should be understood,however, that the invention is equally applicable to the separation ofwax from any overhead or residual lubricating stock from any other typeof crude, treated or untreated.

Propane that is used in this specification is illustrative only ofnormally gaseous substances which may be liquefied to serve asdiluent-refrigerants in this type of a dewaxing process. I prefer to useordinary commercial propane which may contain ,a' fraction of a percentof ethane and 8% or 10% of isobutane and/or normal butane. The propanemay contain larger amounts of butane, and it may contain unsaturatedssuch as ethylene and propylene. Also, I may use liquefied normallygaseous substituted hydrocarbons, such as methyl chloride, dichlordifiuor methane, etc., or I may use normally gaseous ethers such asmethyl ether or amines such as dimethylamine. The word propane as .usedthroughout this specification should not be limited to that particularcompound but should be understood broadly to include the equivalentsthereof. In other words, propane will be'considered to mean a liquefiednormally gaseous diluent-refrigerant compound" or mixtures of compounds.

Referring to the drawing, propane in storage tanks 10 may be transferredthrough pipes 11 by means of pump 12 to mixer 13, which may be providedwith steam coil 14 for effecting complete solution of both oil and waxinthe propane. The waxy oil stock from storage tank 15 is withdrawnthrough discharge heater 16 in pipe 17 and then forced by pump 18through pipe 19 to the mixer 13. From mixer 13 the solution of oil andwax in propane is discharged through pipe 20 and valve 21 into the firstchill chamber 22 (valves 23, 24 and 26 being closed), which has beenpreviously heated in a manner which will be hereinafter described.

When the first chill chamber is about threefourths filled valve 21 isclosed, valves 24 and 25 are opened and valves 26, 27 and 28 are "Washpropane collector 58.

closed, thereby allowing propane vapors to pass through pipes 29 and 30to second chiller 31. This second chiller is at a low temperaturebecause of the chilled mixture which has just been removed therefrom.Consequently, propane vapors condense in this chamber very rapidly, andin ten or fifteen minutes the first chamber has been cooled about thirtydegrees and is exactly at the same temperature as that of chiller 31 andconduit 32, which may be considered as a part of the second chiller.

When equilibrium has thus been established, valve 23 is opened therebyallowing the slurry from the first chiller to pass by gravity throughpipe 32 to the second chiller. When the transferis complete valves 23,24, 25, 28, 34 and 35 are closed and valves 27 and 33 are opened. Itshould be understood that the third chiller which has been emptied of apreviously cooled batch, is cooled to about -40 F.

The second and third chillers, being thus connected through vapor line3'7, rapidly reach equilibrium, propanevaporizing from the secondchiller to lower the temperature thereof and condensing in the thirdchiller to raise its temperature. When equilibrium is finally reached,valve 28 is openedso that the chilledslurry may pass through pipe 38 tothird chiller 36. Valves 2'7, 28 and 33 are then closed and valve 34 isopened so that the fin'al chilling in the third chiller may be effectedby the removal of propane vapors through pipe 39 and low pressure gasline 40. This low pressure gas line is connected to the inlet side ofcompressor 41, which compresses the propane and forces it through pipe42, condenser 43 and pipe 44, which leads back to propane storage tanks10.

When the slurry in the third chill chamber has reached about 40 F.,valve 34 is closed, valve 35 is opened and the slurry is dropped intomix tank 45. From the mix tank the cold slurry is forced by pump 46through pipe 47 and open valve 48 into closed filter 50. .The pressureis rapidly increased in the closed filter until it reaches about 40pounds/square inch, after which time it gradually tapers off to about 65pounds/square inch. The filter element 51 may be the usual canvas clothsupported by suitable screens and firmly clamped around its edges. Thefiltrate passes through pipe 52 and valve 53 to filtrate collector 54.

When a sufficient cake is built up on the filter element, the slurry inthe closed filter is displaced by means of wash propane introducedthrough pipe 55, valve 48, pipe 47, and valve 56 baclcto mix tank 45.Valve 48 is then closed, the first propane wash which carries largeamounts of oil is sent to the filtrate collector through valve 53, andsubsequent quantities. of used wash propane are conveyed through pipe 57to used After the washing step the valve in pipe 55 is closed andpropane in the filter is displaced by gas pressure or otherwise throughpipe 47, valve 59 and pipe 60 to used wash propane collector 58 (valve56 being closed) After the wash propane has been displaced from filter50 the Wax cake is discharged from filter element 51 by means of blowingback or any other suitable means, and it is discharged through valve 49to conduit 61, which may contain a screw conveyor or other suitabletransfer means for conveying the wax slurry to a suitable stripper forremoving diluent and returning it to the system.

The filtrate from collector 54 may be forced bypump 62 through pipe 63and heat exchanger 64 to cool the wash propane, after which it is passedthrough pipe 65 to high pressure stripper 66 which is heated by steamcoil 6'1. Propane is removed throughpipe' 68 and the oil passes throughpipe 69 and reducing valve 70 to low pressure stripper '11 which isheated by steam coil 67. Some direct steam or other stripping medium maybe used to insure the removal of propane .trom the oil in the lowpressure stripper. The dewaxed oil is finally removed through pipe 72 tosuitable storage tanks not shown.

Propane from the top of low pressure stripper 71 is removed through pipe73 to low pressure gas line 44. Likewise, propane from the top offiltrate collector 54 is conducted by pipe 74' to low pressure gas line$0, and propane from used wash propane collector 58 is conducted theretoby means of pipe 75. In short, low pressure gas line' 40 is connected-toall of the equipment which must be maintained at about 35 F. or 40 F},or from, which all propane should be removed. Q

The used wash propane from collector 58 may be returned by pump 76through pipe '17 and valve '78 to pipe 20, through pipe 77 and valve '79to pipe 32, or through pipe 80 and valve 81 to pipe 38. In other words,this used wash propane may be added to the propane-oil mixture at anystage of the cooling, and I prefer to add this propane at the stage atwhich its temperature is the same as that of the slurry undergoingcooling.

It will be observed that the second and third chillers are heated bypropane vapors from the first and second chillers respectively, but,that no means has so far been described for heating the first chiller.heated by steam. I may,-however, close valves 21, 23, 24 and.82, andopen valves 26 and 83 so that propane from the high pressure stripperperature up to that of the incoming solution of oil and wax in-propane.I may also, of course, close valve 85 and open valve 86 and pass propanedirectly from the compressor to the first chill chamber 'or I may simplyopen valve 87 and conduct propane vapors from the top of the storagetank 10 through conduit 88. In any case, it will be observed that I heatup the first chiller by condensing the propane directly therein, andthis is particularly effective when the propane is from the highpressure stripper 66.

It 'may be that the heat capacityof the chill chambers is not enough tocondense the requisite amount of propane or to efiect the desired amountof chilling in three stages, and it should be understood that any numberof cooling stages may be used. Usually the mass of iron in the chilleris greater than that of the propane-oil mixture and two to four stagesof cooling are suficient. Also, I may supplement the chilling byremoving some vapors through pipe 89in amounts regulated by valve 90.

The operation of my invention will be apparent from the description ofthe apparatus. I may introduce about three parts by volume of propanewith about one part by volume of oil into the first chill chamber at atemperature of about90 F. (the chill chamber having been previouslywarmed by the condensation of propane vapors therein). The condensedpropane in the first chill chamber may increase the rela- This chillermay, of course, be

tive volume of propane to oil to about four or five to, one. The emptiedsecond chiller may be at a temperature of about 20 F., and when thefirst and second chillers are connected through conduit 30, both ofthese chillers may reach a temperature of about 60 F., at whichtemperature the slurry may be transferred from the, first chiller to thesecond chiller. In the meantime, the batch in the third chiller has beencooled by withdrawal of vapors through conduit 39 to a temperature ofabout 40 and emptied, and when the second chiller is connected to thethird through conduit 37, equilibrium is reached at a temperature of 20,at which temperature the slurry is transferred from the second chillerto the third chiller. The temperature of the slurry in the third chilleris finally lowered to about 40 by withdrawal of vapors through pipe 39by compressor 41,and the second'chiller, which is now back to- 20,isready to be used once more to condense propane from the first chiller,the first chiller having been warmed up before the introduction of thecharge by warm high pressure propane vapors from stripper 6B.

A most important featureof the invention "is the method of avo'dingshock chilling without excessive loss of re rigeration, thereby.efiecting a very great saving in compressor costs; The metal in eachchill chamber will probably weigh more than all of the propane and oilwhich it contains, and by this systemb! warming up the chill chambers bycondensing propane vapors therein I may raise and lower the temperatureof this enormous mass of metal at practically no cost and without greatheat losses.

Another very important feature is that I maintain my diluent ratiosubstantially constant throughout the several chilling stages. In otherwords, the diluent-evaporated from the first chiller and condensed inthe second chiller is reunited with the slurrybefore the cooling in thesecond chiller is initiated.

By connecting thevapor spaces 0 successive chilling tanks, ashereinabove desc ibed, I insure absolute equilibrium of both temperatureI and pressure and Iiind that this equilibrium is established in 'asmall time interval, usually about tento fifteen minutes. The balancingof temperatures and pressures is automatic and tool-proof, and besidesthe substantial savings in compressor costs and in steam and condenserwater requirements, I- positively avoid shock chilling and am enabled tocarry out the entire process rapidly and smoothly without interruption.l 1

Whi e I have described in detail a preferred embodi ent of my inventionit should be under stood that I do not limit myself to the detailshereinabove set forth except as defined by the following claims whichshould be construed as broadly as the prior art will permit. It may benecessary, for instance, to regulate the flow of gas from one chillchamber to thenext so that,

a desired cooling rate of about 3? per minute may be obtained. Two ormore chillers may be employed and I may use any number of stages.Filters, filtrate collectors, etc. may be replaced by any equivalentmeans, and any of these elements may be modified in accordance withengineering practice familiar to those skilled in the art.

that the description of the invention might be clearly and conciselystated.

I claim:

1. The method of preventing shock chilling in a propane dewaxing systemwherein a diluted oil-wax mixture is chilled in a plurality of stageswhich comprises connecting the vapor space of one stage to a followingstage whereby propane vapors from the first stage are condensed in thesaid following stage to bring about equalization of both pressure andtemperature, and subsequently transferring the cooled slurry from thefirst stage to said following stage wherein it is re-combined with thecondensed propane.

2. In a propane dewaxing system wherein chilling of a diluted oil-waxmixture is effected in a plurality of stages, the method of chillingwhich comprises removing chilled slurry from a latter stage, connectingsaid stage with the top of a prior stage whereby propane vapors from theprior stage may be removed and condensed in the latter stage, allowingthe two stages substantially to come to equilibrium and thereaftertransferring the slurry from the prior stage to the latter stage.

3. In a propane dewaxing system, the method of chilling a dilutedoil-wax slurry which comprises a plurality of transfers between stagesin the manner set forth in claim 2.

ROY N. GILES.

